Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$245.38	11.787%	$274.3029	$274.30	$274.30	$274.30
Purchase #2	$56.72	10.219%	$62.5162	$62.52	$62.50	$62.50
Purchase #3	$82.78	8.856%	$90.111	$90.11	$90.10	$90.10
Purchase #4	$172.49	13.503%	$195.7813	$195.78	$195.80	$195.80
Purchase #5	$91.50	8.312%	$99.1055	$99.11	$99.10	$99.10
Purchase #6	$128.57	5.137%	$135.1746	$135.17	$135.15	$135.20
Purchase #7	$166.62	9.259%	$182.0473	$182.05	$182.05	$182.00
7 purchase totals =	$944.06		$1,039.0388	$1,039.04	$1,039.00	$1,039.00